Leonardite and humus shales are sources of naturally-occurring humate material. Leonardite is a coal-like deposit having either a black, brown or blackish-brown color, containing 25%-90% combined humic and fulvic acids. Typically, leonardite is a low-rank coal derived from terrestrial plant matter, usually found in conjunction with deposits of lignite. It was discovered in 1919 in North Dakota and has been subsequently found in Utah and New Mexico. Usually, leonardite is found as an outcropping of lignite deposits often located close to the surface of the earth.
The origin of leonardite and humic shales is mainly beds of vegetation, though animal life has contributed somewhat to the result. The beds were once beds of vegetation, analogous, in most respects, in mode of formation to the peat beds of modern time, yet in modes of burial often of a very different character. The deposits existed millions of years ago when lush vegetation was abundant. The deposits in some cases were covered by volcanic eruptions, covering the vegetation with a layer of mud and ash to create an "encasement" which prevented the deposit from fossilizing, petrifying, or turning into coal. Water was essentially excluded from the deposit preventing fossilization. These deposits are commonly known as Humus or Organic clays or shales or brown coal.
Humate is characterized as humic matter, which is complex organic molecules formed by the breakdown of organic matter. Humic matter is a class of compounds having variable structure, functionalities and reactivities. Typically, three types of organics, fulvic acid, humic acid and humin, are identified in leonardite and humus shales. The fulvic acid is the acid radical found in the humic matter, which is soluble in alkali and acids. Humic acid is the acid radical found in the humic-humus matter, which is soluble in alkali but insoluble in acid. Humin is the insoluble fraction of humates which is insoluble in both acidic and alkaline solutions.
Leonardite and humus shales have both industrial as well as agricultural uses. In agriculture, leonardite is used as soil amendments and fertilizer. For waste water treatment, metals and organics are filtered using leonardite. Leonardite is also an additive in drilling mud used for drilling oil. For foundry applications, leonardite is an additive to green sand.
Leonardite is commonly known as a source for humic acids. Extraction methods and applications of the humic acids extracted from leonardite are also well known. The extraction methods are based on humic acid and fulvic acid being soluble in alkali, but only fulvic acid being soluble in acid. Several definitions of terms used herein as follows:
Humus is the product of the decay of organic matter and contains both humic and non-humic material.
Humic matter is completely decomposed organic matter, and is readily soluble either in acids or bases.
Humic acids is the collective name for the acid radicals found in humic matter, they may be separated from humic matter by alkaline extraction.
Humates are the salts of humic acids, collectively, of the salts of humic acids specifically.
Fulvic acid is the acid radical found in humic matter which is soluble in alkali, acid, and various alcohols.
Fulvates are the salts of fulvic acid.